The present invention relates to electric resistance material for use as a resistor represented by an earth resistor installed in a main transformer or a power generator at a neutral point, a main or brake resistor for a resistance-controlled vehicle, etc.
A resistor shall have the characteristic that its resistivity is not affected by change of the environment but kept at a constant value. However, the resistor is often heated with Joule heat. For instance, a power or vehicle resistor is heated up to 400xc2x0 C. or so due to heavy electric current. Since a metal resistor has the disadvantage that its resistivity increases as elevation of a temperature in general, such high electric resistance material with less temperature dependency of resistivity has been used so far for a power or vehicle resistor.
An Fexe2x80x94Crxe2x80x94Al alloy, e.g. FCH1 or FCH2, is already known as high electric resistance material. Since FCH1 or FCH2 contains 17-26 mass % of Cr and 2-6 mass % of Al, its resistivity is high with less temperature dependency. However, FCH1 or FCH2 is ferromagnetic, so that a magnetic field is generated by electric current through a resistor. The magnetic field causes vibration of the resistor and occurrence of noise. The vibration and noise can be inhibited by use of non-magnetic material, e.g. NCH1, NCH2 or NCH3, as a resistor. However, NCH1, NCH2 and NCH3 are expensive due to inclusion of Ni at a high ratio and also inferior of hot-workability due to deformation resistance at an elevated temperature as well as occurrence of surface defect (sleaver defect) during hot-rolling.
By the way, stainless steel such as SUS304, which contains 18 mass % or so of Cr, has resistivity of 70 xcexcxcexa9xc2x7cm higher than common steel, but the resistivity is greatly varied in response to temperature change compared with conventional electric resistance material. Furthermore, stainless steel SUS304, which is non-magnetic in annealed state, is changed to ferromagnetic state by mechanical deformation. As a result, a resistor, which is manufactured by forming stainless steel sheet to an objective shape, produces big noise due to generation of a magnetic field. Resistivity of stainless steel SUS304 could be made higher by increase of Si and Al contents. But, increase of Si and Al makes steel sheet harder and inferior of bending formability, and also intensifies occurrence of ferromagnetic state.
An object of the present invention is to provide electric resistance material, which is high of resistivity with less temperature dependency and hardly produces noise caused by a magnetic field during flow of electricity, by adoption of alloying design suitable for increase of resistivity and decrease of permeability.
The present invention proposes new electric resistance material, which has the composition consisting of C up to 0.1 mass %, Si up to 5 mass %, Mn up to 6 mass %, 9-32 mass % Cr, 6-25 mass % Ni, N up to 0.2 mass %, 0-3 mass % Mo, 0-4 mass % Cu, 0-5 mass % Al and the balance being Fe except inevitable impurities with the provision that a value A defined by the formula (1) and a value B defined by the formula (2) are adjusted not less than 78 and 14, respectively.                     A        =                              0.008            xc3x97                                          (                                  %                  ⁢                                      xe2x80x83                                    ⁢                  Cr                                )                            3                                -                      0.43            xc3x97                                          (                                  %                  ⁢                                      xe2x80x83                                    ⁢                  Cr                                )                            2                                +                      8.03            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Cr                            )                                +                      6.8            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Si                            )                                +                      10.9            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Al                            )                                +                      0.56            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Mo                            )                                +                      0.92            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Ni                            )                                                          (        1        )                                B        =                              (                          %              ⁢                              xe2x80x83                            ⁢              Ni                        )                    +                      (                          %              ⁢                              xe2x80x83                            ⁢              Cu                        )                    +                      0.6            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Mn                            )                                +                      9.69            xc3x97                          (                                                %                  ⁢                                      xe2x80x83                                    ⁢                  C                                +                                  %                  ⁢                                      xe2x80x83                                    ⁢                  N                                            )                                +                      0.18            xc3x97                          (                              %                ⁢                                  xe2x80x83                                ⁢                Cr                            )                                -                      0.11            xc3x97                                          (                                  %                  ⁢                                      xe2x80x83                                    ⁢                  Si                                )                            2                                                          (        2        )            
The proposed electric resistance material may further contains one or more of Ti up to 0.4 mass %, Nb up to 0.4 mass % and B up to 0.005 mass %.